Sulfamethazine　(SM2)　is　an　antibacterial　drug,which　has　been　extensively　used　in　human　and　veterinary　medicine,　long-term　consumption　of　which　may　lead　to　the　accumulation　of　sulfonamides　in　the　body.　Detection　of　sulfonamides　often　uses　microbiological　approaches,　mass　spectrometry　and　chromatography,　which　are　expensive　and　time-consuming.　Surface-enhanced　Raman　scattering-based　immunochromatographic　assay　(SERS-ICA)　has　been　recently　applied　in　the　detection.　Herein,　a　Janus-labeled　Au　nanoparticle　with　subnanosized　SiO2-monoclonal　antibody　and　SERS　reporter　(DTNB)　modified　simultaneously　(mAbAuNpDTNB)　has　been　developed　in　a　SERS-based　lateral　flow　immunosensor,　which　can　be　used　for　rapid,　quantitative　and　ultrasensitive　detection　of　sulfamethazine　residue　in　milk.　The　mAbAuNpDTNB　exhibits　a　specific　array　on　a　paper　stripe,　which　not　only　identifies　sulfamethazine　but　also　straightforwardly　exposes　the　Raman　reporter　between　the　AuNps　via　self-assembly.　The　detection　sensitivity　of　SERS-ICA　for　sulfamethazine　reached　0.1　pg/mL,　which　was　far　below　the　previously　published　value　by　ELISA　and　the　maximum　residue　limit　set　by　the　European　Union.　The　entire　SERS-ICA　detection　for　sulfamethazine　was　completed　within　15　min.　Furthermore,　high　accuracy　for　this　assay　was　exhibited　in　the　spiking　experiment　with　a　recovery　percentage　of　88.1%-112.7%.　The　results　demonstrated　that　this　SERS-ICA　can　potentially　be　applied　in　point-of-care　testing　as　an　ultrasensitive　and　quantitative　to　semi-quantitative　analytical　method.